1. Field of the Invention
The present invention relates to a bio-degradable/absorbable dental material required for the regeneration of the tissues of a living body attacked by periodontosis.
2. Statement of the Prior Art
In current periodontal treatments of healthy cementum and periodontal ligament attacked by periodontal diseases, hydroxyapatite and calcium phosphate are used as the alveolar bone fillers to be filled in lost periodontal tissues.
However, such treatments are considered to be only effective to prevent periodontal diseases from reaching an advanced stage or recurring to some degrees. In recent years, the Guided Tissue Regeneration Technic developed by Professor S. Nyman et al (University of Gothenburg) from a biological standpoint of view has attracted attention in dental fields. For such epoch-making Guided Tissue Regeneration Technic, it has been reported that certain results are achievable with what is called Goretex membrane which is neither degradable nor absorbable in a living body. See S. Nyman et al, "The regenerative potential of the periodontal ligament--An experimental study in the monkey", J. Clin. Periodontol, 9:257, 1982.
Since Goretex membrane is neither degradable nor absorbable in a living body, it constitutes an alien substance to the living body and is reactive to the tissues. Therefore we must take off Goretex membrane after first treatment and second operation is thus again needed. From such a standpoint of view, a report of the studies of using bio-degradable/absorbable membranes for the Guided Tissue Regeneration Technic has been presented. See I. Magnusson et al, "New Attachment Formation Following Controlled Tissue Regeneration Using Biodegradable Membranes", J. Periodontol, 59, 1-6, January, 1988.
However, since a homopolymer consisting of 100% polylactic acid is used as the bio-degradable/absorbable membrane, it is impossible to control both dynamic (or mechanical) properties and a rate of hydrolysis simultaneously.
Due to its glass transition temperature higher than a temperature of a body, the homopolymer consisting of 100% polylactic acid gives a physical stimulus to the soft tissues of a living body with the resulting inducement of inflammation. With the homopolymer, it is difficult to freely vary the rate of hydrolysis.
The present inventors have made intensive and extensive studies to eliminate the weak points of the above homopolymer of polylactic acid, i.e., to improve especially its dynamic (or mechanical) properties, thermal properties and the rate of hydrolysis. As a consequence, it has been found that a film or sheet of a lactide/.epsilon.-caprolactone or a glycolide copolymer is best-suited for the Guided Tissue Regeneration Technic. Thus, the present invention has been accomplished.